Introduction. Listeriosis is a foodborne infection, especially dangerous for people in at-risk groups. Susceptibility to listeria infection is determined by a complex of reasons: environmental factors, host immune status, and pathogen virulence. The susceptibility to listeriosis can also be aggravated by previous infections, especially viral infections, which demonstrate a steadily increasing number of identified pathogens.The aim of our study was to present molecular and genetic characterization of pathogens causing sporadic invasive listeriosis in a megalopolis, primarily during the peak of influenza and ARVI incidence.Materials and methods. Listeria monocytogenes isolates were collected from 18 hospitalized patients at hospitals in Moscow, from November 2018 to October 2019. The first comparison group was represented by isolates from food products and fish preserves. The second comparison group included previously examined environmental isolates. The clinical isolates were examined by using multilocus sequence typing techniques, including the standard MLST scheme extended by loci of internalin genes. Isolates of the autochthonous genotype (ST7) were compared through whole-genome sequencing and subsequent analysis of the core genome (cgMLST).Results. In cases of invasive listeriosis, 44% of isolates were isolated from patients with listeriosis; 27% of isolates were obtained from patients with meningitis. L. monocytogenes of phylogenetic lineage II prevailed in these groups of cases that occurred when the epidemic threshold for influenza was crossed during the 2018/2019 season. Listeria pneumonia identified in the senior age group occurred during the season of autumn ARVI and was primarily caused by L. monocytogenes of phylogenetic lineage I. The examination of genomes of ST7 isolates demonstrated identity between the core genomes of bacteria isolated from the mother-infant pair. Out of ST7 food isolates most closely related to the clinical ones was the isolate from meat (23 locus differences, the common deletion in the MFS transporter locus). Analyzing invasive listeriosis, the comparison between the list of the identified genotypes and the data from European countries showed that each country had its own specific range of genotypes, though ST7 was detected in all the examined samples.Conclusions. Along with the monitoring of food manufacturing and storage, timely vaccination against seasonal respiratory infections and use of personal protective equipment in public spaces can reduce the risk of listeriosis incidence in at-risk groups.

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